A conventional heated seat assembly is generally structured like seat assembly 112 provided with planar heater 113, or a heating unit, between the surface material 114 and the main pad 115 as shown in FIG. 12. One of the methods of manufacturing such seat assembly includes a method of integrally forming surface material and main pad by bonding the planar heater to the surface material 114 using double-coated adhesive tape followed by foaming and curing of urethane raw material poured into a mold with the surface material 114 provided therein.
Conventionally, as the planar heater used in such manufacturing method, there is one type of the planar heater (for example, as disclosed in Japanese Patent No. 2621437) that is formed by sewing a linear heater to a base material made of cloth such as non-woven fabric and urethane surface cloth as shown in FIG. 13 and FIG. 14. FIG. 13 is an outside view of a conventional seat heater, and FIG. 14 is a schematic view where a linear heater is fixed onto a base material by sewing. In FIGS. 13 and 14, linear heater 117 is sewed to base material 118 by upper thread 119 and lower thread 120, thereby forming planar heater 116.
Also, as shown in FIGS. 15 and 16, there is a planar heater (for example, as disclosed in Japanese Patent Laid-open Application H8-507404) that is formed by sandwiching a linear heater with two sheets of base material such as non-woven fabric having gas permeability. FIG. 15 is a perspective view of the planar heater, and FIG. 16 is a sectional view of the same. In FIGS. 15 and 16, planar heater 121 is formed by sandwiching linear heater 122 from both sides by base materials 123, 124 having through-holes 125. Besides this configuration, it is also possible to bond the linear heater 122 to the surface material 114 by the base material 124 being used as an adhesive film.
In the case of this planar heater, since the base material is provided with the through-holes 125, urethane raw material flows through the through-holes 125 during a production of the seat assembly, and the surface material 114 directly adheres to the main pad 115, thereby improving the adhesive strength.
However, in the conventional method of manufacturing a seat assembly using planar heaters 116, 121, the base materials 118, 123 made of non-woven fabrics or urethane are liable to be impregnated with urethane raw material, and the urethane raw material in the base materials 118, 123 cures without foaming, deteriorating the softness of the seat surface, and as a result, there arises a problem of affecting a seating “feel”.
Also, in the case of planar heater 121, it is necessary to sandwich the linear heater 122 with the base materials 123, 124, and an adhesive layer is needed for the adhesion of two base materials, causing the number of members and the number of production operations to be increased, and there arises a problem of complication in production.
In the conventional method of manufacturing a heated seat assembly, as shown in FIG. 17, surface material 132 and planar heater 134 are disposed in seat mold 131, and then, urethane raw material 136 is poured in, formed, and cured.
However, in the conventional manufacturing method, the planar heater 134 moves and can not be positioned to a predetermined position due to a forming pressure of foam of the main pad 135, and it is unable to obtain an intended temperature of the seat.
Also, as shown in FIG. 18, the planar heater 134 built into the seat assembly is formed into a mat shape by sandwiching linear heater 137 with cloths 138 having through-holes 133, to which impregnation prevention mat 139 for preventing impregnation of urethane raw material and is made of felt or the like is bonded. (For example, as disclosed in Japanese Patent Examined Publication H7-87806).
In this case, since the surface material 132 and main pad 135 are bonded to each other via through-holes 133 during foaming, it is desirable to increase an opening area of the through-holes. On the other hand, if the opening area is increased by enlarging the diameter of the through-holes 133, the linear heater 137 become unable to be precisely fixed by the cloths 138, since the linear heater 137 is sandwiched between the cloths 138 having the through-holes 133. Because of such restrictive condition, the opening area of the through-hole 133 cannot be sufficiently increased, and therefore, the adhesive strength between the surface material 132 and main pad 135 is not strong enough, resulting in a problem of worsening of the “feel” due to a de-lamination of the surface material 132.
Further, since the impregnation preventing mat 139 for preventing urethane raw material from impregnating into the cloth 138 is bonded, the planar heater 134 is not bonded to the main pad 135, and there arises a problem that the surface material 134 de-laminates at a portion where the planar heater 134 is disposed, thereby worsening the “feel”.
Also, an example of a linear heater used for the planar heater is disclosed in Japanese Patent Laid-open Application 2001-87080. The linear heater disclosed is, as shown in FIG. 19, a linear heater 101 formed by braiding a plurality of conductors 102. In a case of this linear heater, the stresses applied to the linear heater 101, for example, due to a load applied when being seated are dispersed to each of the conductors 102 to improve a bending durability. Also, in the Application, as shown in FIG. 20, conductor 102 and core wire 103 formed of steel wire such as a piano wire or a stainless wire are braided to form linear heater 104, or as shown in FIG. 21, the conductors 102 are braided to form heating element 106 by using tow thread 105 such as aromatic polyamide fibers, polyester fibers, and carbon fibers as a center wire, to improve the tensile strength and bending strength.
However, in the case of the conventional linear heater 104, though, the tensile strength of the linear heater can be improved, the bending strength against repetitive bending loads such as the loads applied when being seated is not sufficient. That is, a friction at crossing portions between the core wire 103 formed of steel wire such as piano wire and stainless wire and the conductor 102 causes the conductor 102 to wear and break, and it is unable to sufficiently improve the durability of the linear heater 104.
Also, in the case of the linear heater 106, generation of such wearing and breaking can be decreased, but it is difficult to produce the linear heater 106 by braiding the conductor 104 so as to have tow thread 105 as the center in a production process.